"Inside Michael's apartment, an unusual contraption," Cooper said with drama. "A chamber he sleeps in that simulates high altitude."

And, Cooper added for effect: "He doesn't want anyone to see it, but he was willing to talk to us about it."

Phelps described the weirdness of heading into his bedroom, but then having to enter something else before retiring.

"Once I'm already in my room i still have to open a door to get into my bed," he said, laughing a bit. "It's just like a giant box. It's like 'boy and the bubble.'"

The air he chooses to sleep in is the equivalent of 8,500 to 9,000 feet. And he said it's helping his performance.

Phelps is sleeping in the chamber as a training tool. And the company that provided him with bed, Hypoxico, was singing it from the rooftops Monday -- thrilled that their product not only had a celebrity endorsement, but one mentioned on primetime TV.

And though he didn't want to show it to Anderson Cooper, Phelps was fine with Tweeting a picture of the chamber to thousands of his followers -- a shot of his bed surrounded by a see-through box... his flip-flops at its side.

Matt Formato, the company's director of business development didn't want to reveal to The Sun the specifics of Hypoxico's deal with Phelps. Just that the company sent him the custom chamber last year and if a mere mortal wanted one like it, it would cost about $15,000.

The chamber is supposed to work by creating a low-oxygen environment, which forces Phelps' system to work harder -- and essentially train -- even when sleeping.

Formato said that Tiger Woods is another of their high-profile clients and that a number of endurance runners and boxers also have chambers.

Formato was hoping that the "60 Minutes" mention would undo the misinformation that ran rampant recently when dozens of media outlets reported that Phelps was sleeping in a "hyperbarbaric chamber." That's the odd capsule that Michael Jackson slept in for a time. It does the opposite of what Phelps' chamber does, flooding a body with oxygen.